Crd losing power up steep hill ? Limp mode

[Petapaulmary]

Hi new to posts but following for years. I have hunted this information everywhere but just getting nowhere.

I have a unmodified 2008 3ltr patrol auto. The problem is it seems to go into limp mode when I go up steep hills near my home.
The speed drops off I would be lucky to be doing 15 to 20 kms hour!
the revs don't go up if I put pedal down, even if I lift foot off and reapply it still does nothing.
I sometimes have to put it into 1st gear to get up the hill.
The boost pressure on ultra gauge shows around 12 to 14 psi on average. The power hold switch sometimes comes on by itself and lights up on "hold" also
Still happens even if I put o/d off
It seems to happen more in hotter weather and with aircon on.
Temp on ultra gauge is usually normal at 90 to 93 c. and doesn't vary much
There are no fault codes on the ultra gauge

There is oil leaking out of the turbo inlet pipe to intercooler.?

The air filters have been changed no oil on them and maf sensor appeared clean but I still cleaned with maf cleaner.

It also happened when I was on beach in 4wd low range goes ok then seem to loose power then comes right?

I am going to get auto trans a service any body got any ideas? I don't want to take to dealer yet as they could tell me anything.

Regards

Paul